Distillation is the physical process by which mixtures, based on differences in their volatilities, are separated by boiling. One of the most useful and general methods of preparing alkenes or olefins is based on the dehydration of alcohols with acids. In the following experiment, these principals are used in the distillation of cyclohexanol to remove the resulting cyclohexene from the reaction mixture. An analytical technique, Infrared Spectroscopy, was used for identifying the different constituents in the reaction mixture and purity of product. This intro is basically good, but a bit brief. There are some interesting things to consider along the way.
Please write out the reaction--draw structures--whenever you are doing a reaction in the lab. Always always always!
Procedure:
Green Organic Chemistry- Strategies, Tools and Laboratory Experiments by K.M. Doxsee and J.E. Hutchison,Thompson Brooks/Cole, 2004; pp 129-134. The procedure used can be found at http://greenchem.uoregon.edu/PDFs/GEMsID70.pdf, the only alterations made were not performing procedural steps 6 and 7 to further distill the cyclohexene.
Data/Analysis:
The procedure calls for 0.074 moles of cyclohexanol. Since one can not measure directly using moles, the following calculation was used to convert into useable units (grams in this case).
0.074 moles of cyclohexanol x (100.1588g/1 mole cyclohexanol) = 7.4117g = 7.4g
This mass of cyclohexanol was then measured on the balance (in liquid form). The actual mass collected was 7.418g.
1.80mL of 85% H3PO4 was also balanced and then added to the 50mL distillation flask with the cyclohexanol as per the instructions.
The mixture was headed gently for five minutes, and then the heat was turned up to 35% of maximum output voltage.
The reaction began in the distillation flask and continued while the heat was managed to maintain a rolling boil.
Once the first drop of product entered the receiving vial, the meltemp It's not a meltemp....it's a LabQuest. Right? was activated, recording data points every two seconds for the duration of the experiment. Data points are shown below, including a graph of the temperature trends over the entire reaction.
The product vial was weighed empty and with the purified product.
Empty vial: 24.948g
Vial with product: 27.631g
Product alone: 27.631g - 24.948g = 2.683g
LabQuest Data:
Distillation Temperature.
Temperature Tables.
IR spectra was recorded to evaluate the purity of the product.
Discussion/Conclusion:
In the preparation of an alkene, cyclohexanol was dehydrated by an acid catalyzed elimination reaction. Routinely this reaction is carried out with a strong acid H2SO4 as a catalyst. 85% H3PO4 was substituted in the experiment as this acid is slightly less harmful then typo here left me with an incomplete sentence. The result yields cyclohexene as a product with minimal amounts of water as a byproduct. and the prevention of use of sulfuric acid.
Fractional distillation was used to maximize the yield of the products. Separation of this manor (manner) allows for the distillation flask to be gently heated ensuring an even separation. The copper packed vigreux column allows for the product to reach vapor pressure and precipitate out as a liquid resting on the copper packing while slowly climbing the column. More surface area is added by the copper to prevent the vapor from falling back to the distillation flask. The result is more precision in temperature control while carrying out distillation. The fractional distillation leads to a cleaner separation of the compnents in the distillation pot, because the added surface area results in multiple cycles of evaporation and condensation. So it leads to a cleaner, more complete separation and purer product distilling over into your receiving flask. It's not exactly about temperature control.
Just a technical point here: a Vigreux column has glass nubbies inside. Ours was a packed fractionating column but was not a Vigreux column.
Early in the experiment the distillation flask was being heated slowly at 30 percent power. After about twenty minutes the power was increased to 40 percent. 10 minuets later the foil was removed to check the condensation level in the vigreux column. After no indication of rising vapors the heat was increased once more. Temperatures were recorded after 5 more minutes. Although the power was not increased the recorded temperatures increased rapidly past the boiling point of cyclohexene. To prevent both cyclohexene and cyclohexanol from distilling the heat was removed from the distillation flask. The power was then increased and proper distillation occurred. The product was then placed into a pre-weighed vial. Infrared spectroscopy was used for purity comparison.
After initial viewing of the infrared spectroscopy there was a spike at 3013.12 indicating there was indeed a double bond formed in the reaction. There was also a noticeable dip above that value indicating the presence of water in the products. The spectra from the product was consistent with the cyclohexene infrared spectra from the SDBS besides the OH swoop around 3300.
Heating the reaction mixture at too high a temperature caused the vapor to collect in the top of the distillation adapter, solidify and drop back into the round flask. Once the temperature was reduced proper distillation occurred. However, the initial error could have possibly reduced the amount of product recovered due to collection in the distillation adapter. Another possible error was a small amount of water in the collection flask that was not removed before the distillation process commenced. There was evidence of of a substance in the IR spectroscopy that contained an OH group. This could have also been from the cyclohexanol OH group that was not properly removed during the distillation process due to the rapid temperature increase at the initial portion of the experiment.
Analyzing IR spectrum: good. Analyzing distillation temps: sorta good....I would like to have seen you discuss the meaning of the temperature range a bit more. I am not seeing a discussion of % yield.
Post-Lab Question:
Calculate the atom economy for this reaction. Atom economy is defined on Wikipedia, but essentially is the mass of the desired product divided by the mass of all reactants (don’t include catalysts or solvents in our reaction). <-- phosphoric acid is a catalyst. Don't include it in your calculation.
[Mass C6H10/(mass C6H12OH + mass H2PO4)] x 100
[82.145g/(101.169g + 96.982g)] x 100 = 41.456%
This lab earned the following scores for: format (2/2) style (2/2) data (3/3) quality of result (1/1) quality of reported data (0.5/1) conclusion (1.5/2) error (1/1) PLQ (1.5/2) for a total of 12.5/14.
Introduction:
Distillation is the physical process by which mixtures, based on differences in their volatilities, are separated by boiling. One of the most useful and general methods of preparing alkenes or olefins is based on the dehydration of alcohols with acids. In the following experiment, these principals are used in the distillation of cyclohexanol to remove the resulting cyclohexene from the reaction mixture. An analytical technique, Infrared Spectroscopy, was used for identifying the different constituents in the reaction mixture and purity of product. This intro is basically good, but a bit brief. There are some interesting things to consider along the way.Please write out the reaction--draw structures--whenever you are doing a reaction in the lab. Always always always!
Procedure:
Green Organic Chemistry- Strategies, Tools and Laboratory Experiments by K.M. Doxsee and J.E. Hutchison,Thompson Brooks/Cole, 2004; pp 129-134. The procedure used can be found at http://greenchem.uoregon.edu/PDFs/GEMsID70.pdf, the only alterations made were not performing procedural steps 6 and 7 to further distill the cyclohexene.Data/Analysis:
The procedure calls for 0.074 moles of cyclohexanol. Since one can not measure directly using moles, the following calculation was used to convert into useable units (grams in this case).0.074 moles of cyclohexanol x (100.1588g/1 mole cyclohexanol) = 7.4117g = 7.4g
This mass of cyclohexanol was then measured on the balance (in liquid form). The actual mass collected was 7.418g.
1.80mL of 85% H3PO4 was also balanced and then added to the 50mL distillation flask with the cyclohexanol as per the instructions.
The mixture was headed gently for five minutes, and then the heat was turned up to 35% of maximum output voltage.
The reaction began in the distillation flask and continued while the heat was managed to maintain a rolling boil.
Once the first drop of product entered the receiving vial, the meltemp It's not a meltemp....it's a LabQuest. Right? was activated, recording data points every two seconds for the duration of the experiment. Data points are shown below, including a graph of the temperature trends over the entire reaction.
The product vial was weighed empty and with the purified product.
Empty vial: 24.948g
Vial with product: 27.631g
Product alone: 27.631g - 24.948g = 2.683g
LabQuest Data:
Distillation Temperature.
IR spectra was recorded to evaluate the purity of the product.
Discussion/Conclusion:
In the preparation of an alkene, cyclohexanol was dehydrated by an acid catalyzed elimination reaction. Routinely this reaction is carried out with a strong acid H2SO4 as a catalyst. 85% H3PO4 was substituted in the experiment as this acid is slightly less harmful then typo here left me with an incomplete sentence. The result yields cyclohexene as a product with minimal amounts of water as a byproduct. and the prevention of use of sulfuric acid.Fractional distillation was used to maximize the yield of the products. Separation of this manor (manner) allows for the distillation flask to be gently heated ensuring an even separation. The copper packed vigreux column allows for the product to reach vapor pressure and precipitate out as a liquid resting on the copper packing while slowly climbing the column. More surface area is added by the copper to prevent the vapor from falling back to the distillation flask. The result is more precision in temperature control while carrying out distillation. The fractional distillation leads to a cleaner separation of the compnents in the distillation pot, because the added surface area results in multiple cycles of evaporation and condensation. So it leads to a cleaner, more complete separation and purer product distilling over into your receiving flask. It's not exactly about temperature control.
Just a technical point here: a Vigreux column has glass nubbies inside. Ours was a packed fractionating column but was not a Vigreux column.
Early in the experiment the distillation flask was being heated slowly at 30 percent power. After about twenty minutes the power was increased to 40 percent. 10 minuets later the foil was removed to check the condensation level in the vigreux column. After no indication of rising vapors the heat was increased once more. Temperatures were recorded after 5 more minutes. Although the power was not increased the recorded temperatures increased rapidly past the boiling point of cyclohexene. To prevent both cyclohexene and cyclohexanol from distilling the heat was removed from the distillation flask. The power was then increased and proper distillation occurred. The product was then placed into a pre-weighed vial. Infrared spectroscopy was used for purity comparison.
After initial viewing of the infrared spectroscopy there was a spike at 3013.12 indicating there was indeed a double bond formed in the reaction. There was also a noticeable dip above that value indicating the presence of water in the products. The spectra from the product was consistent with the cyclohexene infrared spectra from the SDBS besides the OH swoop around 3300.
Heating the reaction mixture at too high a temperature caused the vapor to collect in the top of the distillation adapter, solidify and drop back into the round flask. Once the temperature was reduced proper distillation occurred. However, the initial error could have possibly reduced the amount of product recovered due to collection in the distillation adapter. Another possible error was a small amount of water in the collection flask that was not removed before the distillation process commenced. There was evidence of of a substance in the IR spectroscopy that contained an OH group. This could have also been from the cyclohexanol OH group that was not properly removed during the distillation process due to the rapid temperature increase at the initial portion of the experiment.
Analyzing IR spectrum: good.
Analyzing distillation temps: sorta good....I would like to have seen you discuss the meaning of the temperature range a bit more.
I am not seeing a discussion of % yield.
Post-Lab Question:
Calculate the atom economy for this reaction. Atom economy is defined on Wikipedia, but essentially is the mass of the desired product divided by the mass of all reactants (don’t include catalysts or solvents in our reaction). <-- phosphoric acid is a catalyst. Don't include it in your calculation.
[Mass C6H10/(mass C6H12OH + mass H2PO4)] x 100
[82.145g/(101.169g + 96.982g)] x 100 = 41.456%
This lab earned the following scores for: format (2/2) style (2/2) data (3/3) quality of result (1/1) quality of reported data (0.5/1) conclusion (1.5/2) error (1/1) PLQ (1.5/2) for a total of 12.5/14.